Process for preheating and drawing filaments of synthetic linear polyesters



Dec. 29, 1970 I G. BAUER ETAL 3,551,550

V PROCESS FORVPREHATING AND DRAWING FILAMENTS I V OF SYNTHETIC LINEAR POLYESTERS Original Filed Dec. 23, 1965 United States Patent 3,551,550 PROCESS FOR PREHEATING AND DRAW- ING FILAMEN TS 0F SYNTHETIC LINEAR POLYESTERS Gunther Bauer, Bobingen, and Ingolf Jacob, Strassberg, near Augsburg, Germany, assignors to Farbwerke Hoechst Aktiengesellschaft, Frankfurt am Main, Germany, a corporation of Germany Continuation of application Ser. No. 515,967, Dec. 23, 1965. This application Mar. 18, 1969, Ser. No. 808,722 Claims priority, application Germany, Dec. 31, 1964,

0 Int. Cl. B29c i7/02, /00

US. Cl. 264-290 5 Claims ABSTRACT OF THE DISCLOSURE Process of preheating filaments for drawing using conical rollers whereby the increase in diameter of the roll ers compensates for the increase in length during heating. The diameter varies over the length of the roller by 0.5 to 5% and for polyester filaments heating is effected at a temperature in the range of 80 to 150 C. for an exposure time of l to 5 seconds. High speed processing is possible. A uniformly drawn product is achieved.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation of application Ser. No. 515,967, filed Dec. 23, 1965, now abandoned.

The present invention relates to a process for drawing filaments of synthetic linear polyesters.

There has been proposed a variety of processes for the drawing of synthetic filaments. The conventional method consists in drawing the filaments between rollers or pairs of rollers whose circumferential speed differs in proportion to the desired drawing. In these methods, the filaments may not only be cold drawn but also heated to elevated temperatures prior to or during the drawing. The filaments may be heated in a variety of ways. For example, filaments of polyesters may be heated in a hot current of gas or on stationary heating elements or on heated rollers. In order to obtain filaments of a good quality it is essential that the filaments to be drawn be heated uniformly especially when winding rates of more than 1000 meters/minute occur in a rapid drawing process. However, a god quality of the filament necessitates not only a uniform heating but also a careful treatment of the filament throughout the drawing process.

If the undrawn filament is heated on a stationary heated pin, the diameter of the pin is decisive for the quality of the finished filament. For if a small diameter is chosen, not all individual capillaries of the filament are sufficiently heated at the beginning of the darwing process, which leads to short sections of the individual capillaries remaining undrawn and, consequently, to a nonuniform drawing of the filament. If, on the contrary, a too large diameter is chosen, migration of the drawing zone on the heated pin sets in whereby the drawing tension becomes highly irregular thus causing a non-uniform drawing of the filament. However, filaments that have been drawn in a non-uniform manner exhibit a high degree of non-uniformity of the dyestuff affinity which very much impairs the utility of the filaments.

It has also been proposed to heat the filament by passing it in several wraps around a flat heating element and then to draw it on a stationary thin heated pin. In this manner, migration of the drawing zone is prevented and a material of a uniform dye affinity obtained. However, it is a disadvantage of this proces that by passing the filaments in wraps around the thin pin there frequently occur capillary breakages of the filaments.

3,551,550 Patented Dec. 29, 1970 For the careful heating of the undrawn filament there may also be used heated driven rollers in combination with intermediate pins or rollers. In this case, the filament is generally passed around the rollers in so many wraps that slipping of the filament on the rollers is avoided. However, with this arrangement there are only attained uneconomically low drawing speeds unless one is prepared to tolerate substantial variations of the drawing tension :with the attendant disadvantages as mentioned above.

Now we have found that the aforementioned disadvantages can be avoided and uniformly drawn filaments of synthetic linear polyesters especially polyethylene terephthalate, obtained when the undrawn filaments are heated on or between rollers whose diameters increase with respect to the rising number of filament wraps by 0.5 to 5 percent, preferably 2 percent, the filaments being heated for 1 to 5 seconds in a state which is practically free from tension to a temperature within the range of from to C. and then drawn in known manner. When working according to the process of the present invention, the polyester filaments are heated prior to their drawing for 1 to 5' seconds to a temperature within the range of from 80 to 150 C., i.e. to a temperature above their second order transition point. Owing to this strong heating of the filaments to a temperature above their second order transition temperature, the filaments extend owing to the known increase of the thermal coefiicient of expansion above the second order transition temperature (Holzmiiller and Altenburg, Physik der Kuntstotfe, Akademie Verlag, Berlin, 1961, p. 458). The filaments are heated on or between a pair of rollers at least one of which is driven, the filaments being passed around the rollers in several wraps. For the heating of the filaments, the rollers may either be heated or a heating element may be installed between the rollers.

Owing to the conical construction of the rollers used, i.e. the increase of the diameter of said rollers with respect to the increasing numbers of wraps of the filaments, the variation of the length of the filament is compensated, that is to say the extended filament passes in wraps around a roller whose diameter is larger than that at the position of the previous wrap, whereby slipping of the filament on the roller is avoided.

Rollers which fulfill this requirement may be wholly or partially conical or may have a diameter that increases stepwise. The increase of the diameter depends on the temperature of the filament and the attendant extension of the filament. The increase of diameter shall be greater than 0.5 percent over the whole length of the roller and shall preferably amount to about 2 percent. Greater increases of diameter than 5 percent are not required in view of the extensions of polyester filaments observed within the temperature range claimed.

It was not to be expected that the properties of the undrawn filaments would be modified when heating the filaments according to the process of the present invention. The modification manifests itself in such a manner that it is possible after this treatment, in contradistinction to the working method known hitherto, to draw the filaments in a uniform manner to less than 3.5 times, for example to 2 times their original length. Moreover, the drawing tension becomes more uniform so that even in the case of a high drawing rate filaments of a highly uniform dye afiinity are obtained.

When examining the capillaries of an untreated filament under the polarizing microscope with the aid of a compensator according to Berek, asymmetrically distorted isochromates are observed on many capillaries. When examining the same capilaries after having heated them prior to the drawing process in accordance with the process of the present invention, there are only observed symmetrical isochromates.

By the process of preheating the filaments in accordance with the present invention there is obtained a more uniform and improved drawability of the undrawn filament. This fact is illustrated by the following properties of the filament: if a spinning filament obtained by the conventional method is knotted together with an undrawn filament of the same titer which has been treated according to the process of the present invention and if both filaments are cold drawn, the formation of a local neck for cold drawing always occurs first in the case of the lastmentioned filament.

Although the drawing roperties of the polyester filament are improved by the process of heating the filament according to the present invention, neither its degree of crystallinity nor that of orientation are noticeably modified thereby.

The process of the present invention is preferably used for drawing filaments of polyethylene terephthalate which are most interesting from a technical point of view, however, filaments of polyesters of terephthalic acid with 1,4- dimethylolcyclohexane or of copolyesters of terephthalic acid and isophthalic acid or of other copolyesters can also be drawn by the process of the present invention.

The temperature and the residence time advantageously to be applied in each case during the process of preheating depend on the intended use of the finished filament. It has proved to be advantageous, for example, to draw filaments of polyethylene terephthalate of high strength at a temperature ranging from 80 to 95 C., that is to say at a temperature situated only about 10 to 20 above the second order transition temperature of the filaments, while filaments having a high elongation are preferably drawn at a temperature ranging from 110 to 130 C.

Temperatures within the range of from 115 to 135 C. have proved to be suitable for filaments to be used in the textile industry which must have a specific strength of about 4 to grams per denier, combined with an elongation not exceeding 30 percent and a heat shrinkage at 200 C. of about 18 percent. The filament drawn in this manner has already such a high degree of crystallinity that it can be used for many purposes without further fixation. The latter advantage is very important when winding up filaments drawn at high speed since a heated roller rotating at high speed, as it is used for fixation, can be maintained at constant temperatures with difficulty only. This difficulty is overcome by preheating and drawing the filament in accordance with the process of the present invention, according to which the filament is heated at the relatively low feed-in speed, which process of preheating renders heating of the series-connected take away for the purpose of fixation superfluous.

It is, moreover, an advantage of the process of the present invention that, when the heated filament is withdrawn from the rollers for the purpose of drawing, it is no longer necessary to use an especially thin pin for fixing the drawing point which often causes capillary breakages, since drawing takes place in a uniform manner also without the use of said pin.

When using the process of the present invention, heating and drawing of the filament, moreover, take place at such high speeds that the filament, heated to drawing temperature immediately after the spinning process, can be drawn without previous winding up. The final winding up of the drawn filament may, therefore, take place at winding speeds within the range of from 1000 to 4000 meters/ minute.

The process and apparatus according to the invention will now be described by way of example, with reference to the accompanying drawing in which FIG. 1 is an end elevation and FIG. 2 a plan elevation of a drawing device. The undrawn filament is first fed to an unheated step roller 1 which is driven by a motor, passed around said step roller in the manner shown in FIG. 1, and then led over a fiat heating element 2 to an unheated step roller 3 which is not driven. The first step of the two step rollers 1 and 3 partially has a conical shape. The filament is passed in several wraps around step rollers 1 and 3 and over the flat heating element whereby the filament warms up and extends. The variation of the length of the filament is compensated by the increasing diameter of the conical part of step rollers 1 and 3. After the filament has acquired the temperature of the fiat heating element 2, the filament extends no further and, after the last wrap around the first step of step rollers 1 and 3 and the fiat heating element, the filament is led around a stationary heated pin 4 which has a diameter of 60 mm. around which it is passed to the extent of 1 /2 wraps. From pin 4 the filament is led over the second step of step rollers 1 and 3 and is drawn by these rollers which rotate at a higher peripheral speed, the filament being passed in several wraps around the second half of step rollers 1 and 3 to prevent slipping.

The following examples serve to illustrate different modifications of the invention, but they are not intended to limit it thereto:

EXAMPLE 1 Dried polyethylene terephthalate having a specific viscosity of 860 (measured in a solution of 1 percent strength by weight in a mixture of phenol/tetrachlorethane 3:2 at 20 C.) was melted in an extruder and forced, at a rate of 163 grams/minute, through a nozzle having 200 orifices and a temperature of 290 C. After having passed through a height of fall of about 4 meters, the bundle of filaments was finished with a preparation agent in the conventional manner and passed around a pair of rollers heated at C. to the extent of 16 wraps in the form of an 8. The rollers had a peripheral speed of 240 meters/ minute. The initial diameter of the rollers was 190 mm. which increased with respect to the increasing number of wraps by about 4 percent to 198 mm. The axes of the rollers formed an angle of about 11 with one another which provided the necessary distance of the individual wraps from one another. The time interval between the delivery of a point of the filament to the pair of rollers and the withdrawal amounted to about 5 seconds.

On leaving the said pair of rollers, the filament was drawn in the conventional manner by means of seriesconnected pairs of rollers in two drawing stages to 6 times its original length, and then wound up.

The filaments thus obtained, which had a tier of 1000 deniers, had a strength of more than 7 grams per denier with an elongation of 10 to 15 percent and may be used for the manufacture of fishing-nets, safety belts and the like.

Comparative example If, instead of the conical rollers, cylindrical rollers were used in the conventional manner under otherwise identical conditions, the threadline on these rollers was so unsettled that it was impossible to draw the filament in a uniform manner. If the filament was passed around these rollers to the extent of about 5 wraps the threadline became smooth, however, the drawing tension fluctuated to such an extent that capillary breakages, entanglements and filament breakages occurred frequently.

EXAMPLE 2 This example was carried out with the use of the same raw material, the same drawing device and under the same spinning conditions as those described in Example 1. The pair of heated rollers had a temperature of C. and a peripheral speed of 500 meters/minutes. The filament was passed around these rollers to the extent of 17 wraps in the manner as described before, then it was drawn to two times its length and wound up at the rate of 100 meters/minutes.

The filament thus obtained had a strength of about 1.5 grams per denier with an elongation of percent and had a uniform dye affinity. Safety belts having an especially high capacity to destroy the a-ccelerative force by irreversible elongation can be made from such filaments.

Comparative example If these conical rollers were not used or if the filament was passed around the rollers in a lesser number of wraps, while operating under otherwise identical conditions, a filament was obtained that was partially drawn in the plastic state, that means without orientation, and partially it was drawn under orientation. The filament, therefore, exhibita temperature of from 80 to 150 C. and thereafter drawn the improvement comprising preheated the undrawn filaments to a temperature of from 80 to 150 C. In from 1 t seconds without substantial change in tension during preheating on or between at least two spaced rollers around which the filaments are Wrapped, the diameters of the rollers increasing as the number of filament wraps increase, the increase in diameter over the length of each roller being between 0.5 and 5 percent and the filaments being passed first around that end of the roller having the smalled 50 g irregularities of its teXtile Properties and y 1O er diameter and withdrawn from that end having the largaflinity that it Was useless. er diameter whereby the increase in filament length occur- EXAMPLE 3 ring during preheating is compensated for by the increase in the diameter of the rollers thereby maintaining sub- Spinning filaments, obtained from polyethylene terephstantially constant tension and avoiding slippage of the thalate with a specific viscosity of 790, which had a titer filaments and, after preheating, drawing the so heated of 153 and consisted of individual capillaries, were filament. drawn under the following conditions on the drawing de- 2. The process according to claim 1 wherein the filavice as described in Example 1: ments are heated on the rollers.

Draw-in speed on Temper- Speed on heated ature drawing rollers, of the Number rollers, Uniformity meters/ rollers, of meters/ ofd e minute wraps minute receptivlty Specimen:

422 95 9 1,490 Bad. 422 105 16 1,490 Good. 422 110 9 1,490 Very good. 400 120 9 1, 490 Do.

The residence time of the filaments on the heated rollers 3. The process according to claim 1 wherein the filawas 2.7 seconds in case (b) and 1.5 seconds in case (c). ments are heated between the rollers. When using the same drawing ratio, higher residence times 4. The process according to claim 1 wherein the filaand temperatures yielded lower strength and higher elonments are preheated immediately after spinning without gation values. In order to obtain good textile properties previous winding up. when working under the conditions as indicated under 0 5. The process according to claim 4 wherein winding (d), the drawing ratio must be increased. In this case the up of the drawn filament takes place at winding speeds aforementioned crystallization process sets in which rend- Within the range of 1000 to 4000 meters/minute. ers fixation after the drawing process superfluous. V

EXAMPLE 4 References Cited An undrawn spinning filament, as described in Example UNITED STATES PATENTS 3, was drawn by means of the device shown in the attached 9 9 M itZ t a1- 264210 drawing. Above and below the heating element 2 were in- 2,553,127 1951 Barker 28-713 stalled step rollers whose first steps partially had a 2 45 3,346 1 1959 Pauls n 264290 percent conical shape. A liquid flowed through heating ele- 2,952,879 9/ 1960 KitSOn et a1. 264290 ment 2 which was thereby heated at 120 C. The fila- 3,030,173 4/ 1962 KllrZke t 3. 264290 ment was passed around the heating element 2 and the 3,077,004 2/1963 Mummery 264290 first steps of rollers 1 and 3 to the extent of 10 wraps. 3,216,187 11/ 1965 Chantry ell 1 0 The series-connected stationary and heated pin, on which 3,229,015 1/ 9 Kramer 264-290 the filament was drawn, facilitated the threading by a re- 3,242,248 3/ 966 T rra 264-290 tarding action. Said pin was likewise heated at 120 C. and had a diameter of 60 mm. It the filament, that had been FOREIGN PATENTS treated in the aforementioned manner, was drawn on the 597,765 5/1960 Canada 264 29 second steps of rollers 1 and 3 to 3.5 times its original length and if it was withdrawn at a draw-01f speed of JULIUS FROME, Primary EXaIniIlel 530 meters/minutes, it ossessed 00d textile r0 erties and a good dye affinity p g p p H. MINTZ, Asslstant Examiner We claim: 1. In the process of drawing filaments of synthetic CL linear polyesters wherein the filaments are preheated to 

